Some designs of mobile communication devices—such as smart phones, tablet computers, and laptop computers—contain one or more Subscriber Identity Module (SIM) cards that provide users with access to multiple separate mobile telephony networks. Examples of mobile telephony networks include Third Generation (3G), Fourth Generation (4G), Long Term Evolution (LTE), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Wideband CDMA (WCDMA), Global System for Mobile Communications (GSM), and Universal Mobile Telecommunications Systems (UMTS).
A public land mobile network (PLMN) is a mobile telephony network controlled by a specific network operator. A PLMN may be defined by a unique combination of a mobile country code and a mobile network code that is assigned to the network operator. Each SIM on the mobile communication device may support a subscription that is used to register with and communicate over a PLMN using a corresponding radio access technology (RAT). For example, a subscription may use a LTE RAT to communicate with a PLMN that supports LTE communication. A mobile communication device may include multiple SIMs (a multi-SIM communication device), and each SIM may utilize one or more RATs to communicate with its respective network.
Before a mobile communication device can acquire service through a mobile telephony network, the mobile communication device conducts a PLMN search. The PLMN search includes scanning the entire communications frequency space for network signals. If the mobile communication device is capable of utilizing multiple RATs (e.g., a multi-SIM mobile communication device), the PLMN search is conducted for each RAT that the mobile communication device is capable of utilizing. For example, if a mobile communication device can communicate through GSM, WCDMA, and LTE RATs, the mobile communication device conducts separate PLMN searches for GSM signals, WCDMA signals, and LTE signals.